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follow this subject out further now because it is part of a larger one, which deals with the atmospheres and densities of all the bodies of our system, and to discuss it at length would lead me too far from the present subject; suffice it to say that the enormous atmospheres of Saturn and Jupiter and the absence of a lunar atmosphere result from one single cause, that cause being if I mistake not the chemical constitution of the exterior parts of the solar nebula as each planet was thrown off, and the subsequent action on each globe.

To come to details. Whether the walled plains are really due to volcanic action or not, our authors offer no opinion beyond referring to the hypothesis of Prof. Dana, as being the most rational. Dana suggested that, as at Kilauea, the lava was simply boiling, and gradually extending its boundaries from a centre, so that at last, if the heat continued, a quasi-crater might be formed of any extent. That the smaller craters are true craters Messrs. Nasmyth and Carpenter take great pains to show, and their evidence is of the closest and most satisfactory kind. The woodcuts which we produce will show how the central cones, which are scarcely ever absent in the craters we are now discussing, have originated on the theory advanced ; at the same time it is shown how, on this idea, even when the central cone is absent or the crater is filled to the brim, as in the case of Wargentin, one of the most curious of lunar objects, the effects observed may be explained.

Mr. Nasmyth long ago illustrated the bright streaks on the moon by the experiment which he here details, and a very striking one it is. He took a glass globe, filled it with water, and having hermetically sealed it, plunged it into warm water, "the enclosed water expanding at a greater rate than the glass, exerts a disruptive force on the interior surface of the latter, the consequence being that at the point of least resistance the globe is rent by a large number of cracks diverging in every direction from the focus of disruption."

From the photograph, it is clear that the result is strikingly similar to the rays which have Tycho for a focus, and on the strength of this similarity the authors claim this as another effect of expansion due to cooling. I so, however, the experiment with the glass globe is not in point. But however the cracks were produced, they imagine that thus having them travelling along for hundreds of miles irrespective of surface inequality, there was an up-flow of molten matter which spread out on both sides and turned the narrow crack into a broad streak.

I trust I have said enough about this book to induce all interested in physical problems to peruse it for themselves; it is altogether an admirable production, and if space permitted each picture even would merit a special paragraph.

J. Norman Lockyer

LETTERS TO THE EDITOR

{The Editor does not hold himself responsible for opinions expressed by his correspondents. No notice is taken 0/ anonymous communications. ]

Natural Selection and Dysteleology

In his reply to a criticism which appeared in Nature, Prof. Struthers alluded to a question oi considerable interest to evolutionists, viz., whether or not the presence of use

less organs "proves too much for the argument." * The difficulty is one often met with, and has been well stated by Prof. Huxley, thus :—" Prof. Haeckel has invented a new and convenient name, 'Dysteleology,'for the study of the 'purposelessnesses' which are observable in living organisms—such as the multitudinous cases of rudimentary and apparently useless structures. I confess, however, that it has often appeared to me that the facts of dysteleology cut two ways. If we assume, as evolutionists in general do, that useless organs atrophy, such cases as the existence of lateral rudiments of toes, in the foot of a horse, place us in a dilemma. For, either these rudiments are of no use to the animal—in which case, considering that the horse has existed in its present form since the pliocene epoch, they surely ought to have disappeared—or they are of some use to the animal, in which case they are of no use as arguments against teleology," &c+

Now it appears to me (as I think it must to all upon adequate consideration), that the dilemma thus presented is only apparent; its first-mentioned horn having no existence. In other words, we can never in any single case be sure that any length of time would have been sufficient to enable natural selection totally to obliterate a useless organ.

Mr. Darwin, in the "Origin" and in the "Variation," has mentioned three causes which operate towards the removal of useless structures. These causes are Selection, Disuse, and Economy of Growth. Recently he has suggested a fourth cause, which may be epitomised as the dwarfing influence of impoverished conditions, progressively reducing the average size of the useless structure, by means ot free intercrossing. J I shall endeavour to show that these causes are not sufficient to obtain the complete extinction of rudimentary parts in all cases.

Selection may be considered as applying only to those rare instances in which changed conditions of life may be supposed to have rendered a previously useful organ injurious; for so far as selection operates in obliterating a merely useless organ, it will be more convenient, for the sike of brevity, to identify it with the Economy of Growth. § Since, however, it is obvious that an injurious organ must pass through the merely useless siage before it becomes wholly suppressed, we may dismiss this cause without further comment.

Disuse and Economy of Growth are so much entangled in their operation, that it is hopeless to find examples illusliating their separate action. In so far, therefore, as we choose to disentangle them, we must discuss the question in the abstract.

Disuse may be left out of the qujstion, so far as its influence is due to the principle of inheritance at corresponding periods of life; for, as Mr. Darwin tersely observes, "as most organs could be of no use at an early embryonic period, they would not be affected by disuse; consequently they would be preserved at this stage of growth, and would remain as rudiments." i| It may,

* Nature, vol. ix p. 83.

t "Critiques and Addresses," pp. 307-8.

I Natire, vol. viii. pp. 432 and 505.

§ 1 think, also, that if the Economy of Growth is really a principle independent of the "more general principle," viz., the direct influence of " natural selection in continually trying to economise every part of the organisation" (Compare "Origin," 1873, pp. 117-18), it may yet, without any great stretch of inference, be considered as due to the indirect influence of natural selection. For, the survival of the fittest demands that each individual shall utilise its stock of nutriment to the best advantage : and, this demand being continued through many generations, it does not seem in itself improbable, that it should thus at last secure to all the members of the surviving species an inherited tendency so to economise their nutritive power when fresh occasion requires—an advantageous innate trmperatnent distinct from the external elimitutlire agency of Natural Selection. Only in some such way can we account tor the (acts of acclimatisation, in those cases where the adap ive changes take place immediately after the transportation of the organism: also for an analogous class of facts, such as that of the shells in the same species of Mollusca, differing in their thickness upon the weather and the Ice sides of the Plymouth breakwater.

|] "Variation," vol li. p. 317. I may mention, also in passing, that it seems to me not tinopen to question whether disuse is the principal cause even of reduction There is no doubt that disuse causes more or iess of atrophy in the individual, and from this tact it is argued, that the principle of inheritance at corresponding periods of lile mu-t entail the continued reduction of a disused part in the species. Now the only eflect ot the principle relied on is that of prolonging, as it were, the life of the disused part over many generations—thus affording it an indefinite time to succumb to the conditions which reduced it in the lif<: of t' e individual. Hut it is necessary for the validity of the in'cience that it would so succumb, to show that ihese conditions are the efficient causes of this reducing process in the one case, as they prove themselves to he in the other. Suppose, for instance, that failure of nutrition is the principal cause of atrophy under disuse, does it follow when such failure has done, to all appearance, its utmost during the life of the individual (as we sec in disease), that it could do any more were that life indefinitely prolonged? Of course in the case of shott-lived animals, where the dwarfing influences may not have time to exhaust themselves in a single generation, the principle of inheritance at corresponding ages may be drawn however, be objected that the doctrine which Mr. Darwin elsewhere inculcates,* and deems sufficient to account for the total suppression of rudimentary organs, viz., inheritance at earlier periods of life, is faal to dysteleology as a prop to evolution—at least in the case of long-lived species. And so it would be, were not this principle of so shadowy an application that, while it is perfectly legitimate to point to it as a possible cause of total suppression in some cases, it would be simply absurd to argue that such must be its effect in all.

We next come to the Economy of Growth. Suppose an organ to become suddenly useless, this principle would at first cause its rapid reduction. In proportion, however, as its presence ceases to be injurious, the arresting process becomes slower and slower, until a point is reached at which it is presumably nil. That such a point of rest must somewhere be attained seems evident, if we consider that the smaller the diminishing organ becomes the less is it subject to the influence of the Economy of Growth. In other words, when the organ undergoing reduction becomes so minute relatively to the size of the animal (or, more correctly, to the available store of nutrition), that the supply of nourishment it requires is no longer perceived by the organism at large, it then remains permanently of that size. "The economy of growth will not account for the complete or almost complete obliteration of, for instance, a minute papilla of cellular tissue representing a pistil, or of a microscopically minute nodule of bone representing a tooth ;"t and, the whole principle being one of relation, it is a question, for instance, whether the rudimentary digits of a horse consume a greater relative amount of nutrition than does the " minute papilla." Besides, without entering in o details, I think there is very good reason to believe that the Economy of Growth is unable to reduce an organ which was originally large, to the same absolute size as it can an organ which was originally small. From all this it follows, that if the struggle for existence were in any case so keen as to afford Selection [i.e., Economy) the opportunity of totally obliterating every rudimentary organ, it seems probable that the species itself would require to become extinct.

Turning now to the last of the causes propounded by Mr. Darwin, there can be no doubt that it is (theoretically) sufficient to procure total obliteration. Forasmuch, however, as we can never know in any given case whether or not the requisite conditions have been supplied,—i.e. impoverished nutriment for an enoimous length of time,—this newly added cause affords no further justification for the old statement, that the theory of Natural Selection fails to account for all the ficts of Dysteleology.

The perusal of the last-mentioned thoughtful conception has suggested to me the probable existence of another cause, having a more general application; but as it can never induce complete suppression, I shall reserve it for the subject of another communication.

Mr. Mivart supposes that organs may become suddenly aborted J; but, apait from the weighty objections to this view,§ there is no case on record, so far as I am aware, of an organ thus becoming totally suppressed in any domestic species. A sport of this kind always leaves a rudiment, and it is upon the analogy of such sports alone that Mr. Mivart's argument is founded.

Having now enumerated all the causes ever proposed by evolutionists to account for the reduction of useless parts, it is evident that we should antecedently expect to find innumerable examples of such parts in the condition of rudiments. || Indeed the only difficulty is to account for that final disappearance of organs which must, by any theory of evolution, be postulated to have taken place. The solution is afforded by the exhaustive contemplations of Mr. Darwin, for, whether or not we believe in pangenesis, we cannot but deem it in the highest degree probable

upon until the point of such exhaustion is attained ; but is it not open to question whether this point can never be reached at all? It must de remembered, too. that in the case of wild species the effects of disease are always associated with other reducing causes, so that here we may easily over-rate the share it has in the work ; but in the case of domesticated species the effects of disease are much more isolated [in consequence of Economy of Growth, etc., being, to a great extent, in abeyance); and here we find that atrophy of disused parts, although at first very rapid, eventually does not proceed to_ nearly so great an extent as it does in the case of wild species. The question thus raised, however, is of no practical importance, since whether or not disuse is the chief cause of atrophy in species, there is no doubt that atrophy accompanies disuse.

* w Variation," vol. ii. p. 80.

t "Variation," vol. ii. p 397.

J 11 Gene is of Species," 1st ed. p. 103.

} See " Origin," pp. 201—204.

II it is unnecessary to consider the collective action of these causes, for a moment's reflection will now make it evident that none such exists below t he point at which the Economy of Growth ceases to be felt.

that the influence of inheritance is not of unlimited duration. If so, we have at once an adequate cause for the eventual destruction, even in the embryo, of rudimentary parts; but, as it is a cause which would only act after an immense lapse of time, it would have no influence until the original specific type had undergone a considerable modification. Thus, the facts of dysteleology, far from "cutting two ways," afford the strongest confirmation of the natural selection theory; for, as time is thus shown the chief agent in the final destruction of rudiments, and as species are always undergoing change, on the one hand we have an explanation of the fact, that the greater the divergence of the specific type from its original the fewer rudiments do we find of organs characteristic of the latter, while on the other hand, the less such divergence the greater the number of such rudiments— a fact of which the necessary consequence is, that "with species in a state of nature, rudimentary organs are so extremely common that scarcely one can be named which is wholly free from a blemish of this nature." George J. Romanes

The Action of the Heart

Having replied to Mr Garrod's criticism of my "Locomotion of Animals" (nature, vol. ix. p. 281), I now wish to show that the explanation given by him of the diastole of the heart is not in accordance with fact.

In a recent number of Nature (vol. ix. p. 282) I asked Mr. Garrod to explain "how the left ventricle of the heart opens after a vigorous contraction in which all the blood contained in the ventricular cavity is ejected and the ventricle converted into a solid muscular mass, if not by a spontaneous elongation of all its fibres." He replies:—"At first sight it might seem that the active dilatation of the heart during the diastole did depend on an inherent power in the muscular fibres of the ventricles to elongate, but the peculiarities of the coronary circulation are quite sufficient to explain the phenomenon without the introduction of so unnecessary a theory as that of Dr. Pcttigrew. For in the heart when removed from the body, as in the living body dur.ng diastole, the injection of fluid into the coronary vessels causes the whole heart to open up from the congestion of the ventricular walls, and so produce the active dilatation which is well known to occur" (nature, vol. ix. p. 301).

The explanation given by Mr. Garrod of the manner in which the ventricles of the heart open up during the diastole is eminently unsatisfactory. In fact it is no explanation at all. He informs us that the active dilatation of the ventricles is due TM to peculiarities in the coronary circulation" . . . "for in the heart when removed from the body the injection of fluid into the coronary vessels causes the whole heart to open up from the congestion of the ventricular walls, and so produce the active dilatation which is well known to occur."

The coronary vessels, as everyone is aware, simply supply the blood which nourishes the substance of the heart. There is no peculiarity whatever in the circulation of the blood through them. The blood flows through the coronary vessels in a more or less steady stream as through all the other vessels of the body. In other words the substance of the heart is full of blood during the closure or systole of the ventricles, as well as during the opening or diastole of the ventricles. The presence of the blood, therefore, within the coronary vessels can exert no influence in opening up or actively dilating the ventricles. This is proved by direct experiment. If the heart be cut out of the living body and the coronary vessels divided, the ventricles go on opening and closing with the utmost regularity for protracted periods. Here, however, the power which, accordinglo Mr. Garrod, opens the ventricles is inoperative. The same thing happens when the heart is cut out of the body and the vessels Laid open. If, however, the ventricles open and close when the coronary vessels are freely divided, and the blood which is said to distend or open up the ventricles is allowed to escape .from the cut surfaces, it is quite clear that the blood pressure within the ventricular walls can exert no influence whatever in producing the diastole. If blood is not admitted into the coronary vessels, or if admitted it is allowed fieely to escape, it cannot of course act as a distending medium. Allowing, however, for the sake of argument, that the flow of blood through the vessels of the ventricles occasioned the opening or dilatation of the ventricles, it is evident, for the same reason, that the presence of the blood within the ventricular walls, from the fact that the blood is nearly constant

in quantity and virtually incompressible, would prevent the closing or contraction of the ventricles. Mr. Garrod, I opine, is

here on the horns of a dilemma. He evidently puts the cart before the horse. It is the movements of the heart which determine the movements of the blood, and not the converse.

The cardiac movements are due to a change of shape in the sarcous elements or ultimate particles of the muscular fibres of the heart, and in the adult organ can only be effected by a vital and alternate elongation and shortening of all the fibres composing the heart; the elongation occurring during the diastole and the shortening during the systole. Similar remarks are to be made of the voluntary muscles which, as stated in my work on "Animal Locomotion," are endowed with centrifugal and centripetal movements.

That the opening and closing of the ventricles of the heart are in no way connected with the passage of blood through the substance of the organ, is proved indirectly by the movemens of the heart of the embryo. Here the heart opens and clones with time-regulated beat, while yet a mass of cells, and before it contains blood either in its cavities or in its substance. But that the presence of blood is not necessary to such movements is placed beyond doubt, for rhythmic movements occur in the vacuoles of certain plants, as e.g. the Volvoxglobalor, Gomum fectorale, and Chlamydomonas, where no blood is present.

Lastly, if a frog be slightly curarised and its spinal cord destroyed, it is found, on exposing the heart, that the sinus venosus, vena cava inferior, the auricles and ventricles art quite destitute of blood, and yet the organ beats normally and with the utmost regularity. Mr. Garrod has consequently not yet succeeded in answering my query as to how the di stole of the left ventricle is produced He has failed to show that it is not effected by the active elongation or centrifugal movements of all its fibres. J. Bell Fettigrew

Lakes with two Outfalls

Having observed the discussion lately carried on in your pages as to the existence of lakes with two outfalls, I think the following description of such a lake by Prof. Bell, of the Geological Survey of Canada, may be interesting to some of your readers. It occurs on the summit of the high Laurentian country between Lake Superior and Hudson's Bay :—

"In crossing the country from Lake Nipigon to the Albany River, we first followed the Ombabika River to its source, which is in Shoal Lake, three and a half miles long and one mile wide, lying at a distance of twenty-five miles north-east of the mouth of the river. This lake lies due north and south, and discharges both ways, the stream flowing northward towards the Albany, called the Powitik River, being nearly as large as the southern outlet. No portage occurs on the Ombabika for about nine miles before reaching Shoal Lake, nor for nearly five miles beyond its northern outlet; so that we passed the height of land with the greatest possible ease, having had about seventeen miles of uninterrupted canoe navigation, from the time we made the last portage, in going up the southern side, till we came to the first on going down on the northern. Shoal Lake has an elevation of scarcely 300ft. over Lake Nipigon, or about 1,200 ft. above the sea."—" Report of Progiess Geological Survey of Canada for 1871-72," p. 107. George M. Dawson

Montreal, Feb. 19

The Ink of the Cuttle-fish

With reference to the interesting account in Nature, vol. ix. p. 332, of a gigantic Cephalopod captured in American waters, and of a still larger one, which attacked the boat belonging to some fishermen near Newfoundland, by twining its arms round the vessel, and which, having had two of those arms cut off by the fishermen, moved off, ' ejecting a large quantity of inky fluid to cover its retreat," I desire to draw attention to an observation respecting this fluid, which I made on the occasion of a visit to the Crystal Palace Aquarium. My friend Mr. Lloyd was good enough to dislodge a cuttle from its place of concealment, and the usual inky discharge followed, as the crrature shot across the tank. Mr. Lloyd states in his interesting "Handbook to the Marine Aquarium," "that the ink (which is viscid) does not generally become diffused through the water as writing ink would be, but is suspended in the water in a kind of compact cloud till it gradually settles down, and is dispersed in flakes." Now I quite think, with Mr. Lloyd, that this being the case, it is difficult to perceive how, according to the generally received opinion, its retreat is covered by the ejected cloud. It seems to me more likely that this discharge is to divert the at

tention of a pursuer—a dog-fish for instance—which would for the moment be startled by the sudden appearance of masses of dark colour in the water, and in the confusion the cuttle makes his escape.

Now that public aquaria are becoming so general in our great towns, it is much to be hoped that this and many other interesting problems in marine zoology may be solved.

Birmingham, Feb. 28 W. R. Hughes

Transmission of Light in a Squall

On the Admiralty Pier, Dover, during a "squally" gale, I remarked an occasional jerking or unsteadiness in one of the adjacent lights, say two miles off, to one of the coast-guard's men with whom I was talking at the time.

To him this was a well-known observation in squally weather. At times, he said, two lights could distinctly be seen for a second or so; frequently the shape of the light was changed, by elongation, vertically and horizontally.

The above phenomenon, if not generally known, might be worth noticing and verifyin in your excellent paper.

I suppose an explanation is to be lound in the different densities of the atmosphere through which a ray of light must pass in rough unsteady weather; the second image being simply the persistence of the one sren immediately before the change in position of the ray by refraction. James C. Inglis

DR. LIVINGSTONE AND THE CAMERON EXPEDITION

IN Nature for Feb. 26, we expressed the desire which we felt, in common with our readers, for information respecting the orders that have been sent to Zanzibar as to the disposal of Dr. Livingstone's body. We now have great pleasure in being able to announce that Lord Derby acted with the promptitude and energy which might be expected from a statesman who has always shown a warm sympathy for the cause of geography. With the concurrence of the family, his Lordship has sent a telegram ordering the body of the illustrious traveller to be sent to England, and we believe that it is to be accompanied by one or two of Livingstone's faithful negro followers.

The melancholy death of Dr. Dillon and the return of Lieut. Murphy, leaves Lieut. Cameron alone, to proceed to Ujiji, to recover the box of papers left there by Livingstone, and to prosecute further geographical exploration. Heavy unforeseen expenses obliged Lieut. Cameron, who has proved himself to be a resolute and observant explorer, to purchase stores at exorbitant rates at Unyanyembe. The necessity for providing for the march of Murphy and Dillon to the coast, with Livingstone's body and most of his followers, is his complete justification for incurring this unauthorised expenditure, and there can be no doubt that the Geographical Society will treat its gallant emissary in a generous and liberal spirit. Cameron has suffered cruelly from fever and ophthalmia, and he is now resolutely pressing onwards in the performance of his work—the Society's work—in the face of greater difficulties than were encountered by any previous expedition. He carries with him our warmest wishes for his success, and the sympathy of every true geographer in England,

ON THE NEW RHINOCEROS AT THE
ZOOLOGICAL GARDENS

AGLANCE at our list of additions to the Zoological Gardens during the last week will inform the reader that the Zoological Society has been successful in adding to its already unrivalled collection of specimens of the genus Rhinoceros still another species, which is exhibited for the first time in the Society's collection, and most probably in this country.

It is well known amongst naturalists that in Asia there are to be found two species of Rhinoceros, with a single horn developed on the top of the nose. The larger of these is the gigantic Indian Rhinoceros (R. unicornis), many specimens of which have been brought to this country, and a very fine male example of which is living in the Regent's Park Gardens. In it the skin, which is immensely thick, is thrown into massive folds or shields, making the animal appear as if clad in armourplating. Each shield is thickly studded with nearly circular slightly-raised tubercles, which look very much like the heads of innumerable bolts intended to strengthen and retain the shield in position. The folds that surround the neck, where it joins the head, arc very ample, producing the appearance of the now so fashionable ruff, somewhat modified. According to the observations of the late Mr. Edward Blyth, the Indian Rhinoceros is found only at the foot of the Himalayan hills, and in the province of Assam, along the valley of the Brahmapootra.

The second species of one-horned Rhinoceros is generally called the Javan Rhinoceros (A', sondaicus). It is found in Java, and in the country stretching from Malacca up through Burmah to Assam. It is considerably smaller than the Indian species; the shields are not so strongly marked, and are not arranged in an exactly similar manner, the gluteal shield not being completely divided into two by a transverse fold situated half-way down it; and the middle neck fold, instead of running backwards on each side before it reaches the spine, crosses the middle line, and so divides off a saddleshaped shield, which is median, and as deep from before backwards as from side to side. The fold which surrounds the neck is also much less significant, and the head is narrower and less formidable in aspect. The tuberculation of the shields is more slightly marked, and each tubercle is proportionately smaller in diameter.

It is a specimen of this Javan Rhinoceros (R, sondaicus), a nearly full-grown male from Java itself, which the Zoological Society has succeeded in purchasing, and which is now exhibited in the same house as the Indian species, so that every opportunity is at last afforded for a more minute study of the differences which will most probably be found to distinguish the two species.

The other species of Asiatic Rhinoceroses, namely, the Sumatran Rhinoceros (R. sutnatranus), and the Hairyeared Rhinoceros (R. lasiotis), are both two-horned, and have been divided off as a separate genus, that of Ceratorhinus, by Dr. J. E. Gray. The skin is not divided into shields, and is thinner than in the one-horned species. The type specimen of the Hairy-eared Rhinoceros, the only example known, is now living in the Zoological Gardens. About a year ago the Sumatran animal was also represented, and rumour says that the gap caused by its loss will not be long unfilled.

NEIL ARNOTT, M.D., F.R.S.

WE have this week to record the deathof thiswell-known man of science, which took place at his residence in Cumberland Terrace, Regent's Park, on the 2nd inst. He was born at Arbroath in May 1788, and had consequently reached his eighty-sixth year.

While Neil was yet young his father died, and the family removed to Aberdeen. Neil went to the Aberdeen Grammar School, being there with Lord Byron, and succeeded so well in the one thing then taught, Latin, that he gained a bursary by a competition in Marischal College, which he entered in iSot. In his third year he came under Patrick Copeland, Professor of Natural Philosophy, renowned for his admirable course of lectures, and especially for his power of experimental illustration. Arnott was one of Copeland's best pupils, and afterwards turned to full account the careful notes that he had made of the lectures.

He began the study of medicine in Aberdeen, and in 1806 he went to London to prosecute the study.

Young Arnott, while his medical education was still incomplete, went aboard an Indiaman, as assistantsurgeon, making the usual voyage of a trading East Indiaman in those days. He was the intellect and soul of the ship, associating with everyone that could learn or teach anything; he was the resource in all serious emergencies, of whatever kind.

On his return to England, in 1811, he settled as a medical practitioner in London. He was the chief medical adviser to a colony of French refugees who settled in Camden Town, and also became physician to the French and Spanish Embassies, his fluency in languages serving him in good stead. It was about 1823 that he first turned to account his studies in natural philosophy, by giving in his own house a course of lectures both on the general subject and on its applications to medicine. These lectures formed the basis of the " Physics," the first volume of which appeared in 1827, and gained for the author an instantaneous and wide-spread reputation. The first edition was sold in a week after being reviewed by the Times. In a few years five editions were exhausted, and the work was translated into all the languages of Europe. The freshness and popular character of his style recommended the book to the general public, and did not prevent its favourable reception by the highest scientific authorities; Herschel and Whewell both gave emphatic testimonies to its accuracy and originality. The author was thenceforth recognised as a man of science and an inventor of no mean order. His practice as a physician was extended, and he became a Fellow of the Royal Society. On the foundation of the University of London in 1836 he was nominated a member of the Senate, and in 1837 he was named Physician Extraordinary to the Queen.

In 1838 he published a treatise on warming and ventilating, and in this he described the stove since called by his name. He introduced the water-beds, and made many other useful applications of physics to medical and surgical practice. For many years he had withdrawn from medical practice. He had a large circle of friends in and out of the profession. His conversational powers, his large range of scimtific knowledge, and his geniality of manner, will be long remembered by those who now regret his loss.

OZONE*
II.

COME of the properties of ozone have already been referred to. At the common temperature of the atmosphere, it may be preserved, if dry, for a very long time in sealtd tubes, but by slow degrees it becomes changed again into ordinar) oxygen. This conversion goes on more rapidly as the temperature is raised, and at 237 C. it is almost instantaneous (" Phil. Trans." for 1856, p. 12). The alteration of volume which occurs at the same time has been already sufficiently described. A similar effect to that of heat is produced by several oxides, such as the oxide of silver or the peroxide of manganese, which by contact, or, as it is termed, catalytically, instantly change ozone into ordinary oxygen. Ozone is also destroyed by agitation with water, provided the ozone is in a highly diluted state. But the most interesting fact of this kind is one which I have recently observed, and which I hope to be able to exhibit to the Society. Dry ozone, even if present in such quantities as freely to redden iodide of potassium paper, is readily destroyed by agitating it strongly with glass in fine fragments, although, as we have seen, it may be preserved for an almost indefinite period in sealed glass tubes. This experiment, as it appears to me, foims a new and closer link than any hitherto observed between a purely mechanical action and a chemical change.

Ozone is a powerful oxidising agent. It attacks metallic mercury and silver with great energy, and converts them into oxides. The experiment with mercury is very striking, and is a delicate test for ozone, either in the dry or moist state. A few bubbles

* An Address delivered betore the Royal Society of Edinburgh on December 23, 1873, by Dr. Andrews, LL.D., F.R.S., Honorary Fellow of the Royal Society of Edinburgh. (Continued from p. 349.)

of oxygen containing not more than -s^th part of ozone will alter wholly the physical characiers of several pounds of mercury, taking away the lustre and convexity of the metallic surface and causing the mercury to form an adhering mirror to the surface of the glass vessel in which it is contained. If ozone in a diluted state is slowly passed through a tube filled with silver leaf, the metal will be oxidised to the distance of 2 or 3 millimetres, but the oxidation will not proceed further, although the ozone reactions are wholly destroyed. This striking result is due to the catalytic action of the portions of oxide which are first formed. So small is the amount of oxide produced in this case that, in a glass tube through which many litres of electrolytic ozone had been passed, the increase in weight from the formation of oxide only amounted to a scarcely appreciable fraction of a milligramme.

Ozone is absorbed by oil of turpentine, oil of lemon, and other essential oils. These oils have also, like phosphorus, the power of changing oxygen into ozone, while they are slowly oxidising; so that if oil of turpentine is shaken for some time in a flask filled with air or oxygen, the oil will acquire ozone properties.

Ozone decomposes a solution of iodide of potassium, liberating the iodine, which may be discovered by its red colour, or its blue compound wilh starch. If the action is continued sufficiently long, the free iodine disappears from the formation of iodate of potassium and the solution becomes colourless. Reddened litmus paper moistened with a solution of iodide of potassium is turned blue, when exposed to the action of ozone, in consequence of the caustic alkali formed by the decomposition of the salt. In employing this test it will often be found advantageous to remove the free iodine by washing the paper with strong alcohol. This form of the iodide of potassium test has been proposed by I louzeau for the discovery of ozone in the atmosphere. Ozone produces other reactions of a similar character which it will be sufficient here barely to mention. Paper moistened with sulphate of manganese becomes brown when exposed to this agent from the formation of the hydrated peroxide. Solutions of thallous oxide are in like manner converted into the brown peroxide ; the black sulphide of lead into the white sulphate, and the yellow ferrocyanide of potassium into the red salt. The action of ozone on tincture of guaiacum, which it turns blue, was made a subject of special study by Schonbein.

The bleaching properties of ozone are highly characteristic and have attracted a great deal of attention. It deprives indigo of its blue colour, converting it into isatin, and bleaches readily litmus and other vegetable colouring matters. Attempts have been made to apply this property of ozone in the arts, and particularly to the refining of sugar and the bleaching of linen. It has been even stated that these and other applications of ozone, as a decolorizing or bleaching agent, have been successful; but the results of my inquiries on this point have, I regret to say, been unfavourable, and it remains yet to be seen whether this singular body can be made subservient to the useful purposes of life. For the preparation ot ozone on the large scale from ordinary.air, a modification of the tube-generator of Siemens has been proposed by Beanes, and is an efficient and powerful instrument.

I will not detain the Society by an account of the history or properties of the problematical body to which Schonbein gave the name of antozone. He considered this body to be oxygen possessing permanently positive properties, while ozone itself he regarded as negative oxygen. Ordinary or inactive oxygen, according to him, is formed by the union of ozone and antozone. These views have not been supported by recent investigations, which leave little doubt that the antozone of Schonbein is identical with the peroxide of hydrogen of Thenard. From ozone the peroxide of hydrogen can be readily distinguished by the solubility of the latter in water.

Soon alter the discovery of ozone, Schonbein having observed that the air of the country frequently coloured a delicate ozone test-paper in the same manner as ozone itself, inferred that ozone is a normal constituent of our atmosphere. lie concluded that the amount of this body present in the air is different in different localities, and in the same locality at different times, and witli great boldness he attempted to connect its presence or absence with the prevalence or rarity of certain catarrhal affections. A new field fur investigation was thus opened up, which has been assiduously cultivated by a large and zealous bar.d of observers. Belore referring however to their labours, it will be necessary briefly to allude to the present state of our knowledge regarding the existence of ozone in the atmosphere.

Schonbein always maintained that ozone is a constituent of atmospheric air, and his various papers on this subject alone would, if collected, fill a large volume. In his last memoir he observes that the active substance in the air acts in a parallel manner on iodide of potassium and sub-oxide of thallium papers, although more slowly on the latter; and that the thallium paper, which has been coloured brown by the air, behaves towards reagents in the same manner as that which has been exposed to artificial ozone. From these facts he infers that the active substance in the air is neither peroxide of nitrogen nor sulphuretted hydrogen. He further states that the atmosphere never contains free nitric acid, although nitrate of ammonium in small quantities is frequently present ; and that neither chlorine nor bromine can be present in the free state in air, on account of their affinity for hydrogen. Houzeau also maintained that the existence of ozone in the air was proved by the alkaline reaction of iodide of potassium paper, which had been decomposed by exposure to the atmosphere. Although experiments and arguments of this kind were sufficient to give probability to the view that the active substance in the atmosphere which produces these reactions is ozone, they were at the same time far from conclusive, and some of the ablest chemists of Europe accordingly considered the question doubtful, while others attributed the effects observed to the presence of oxidising agents altogether different from ozone. I will only cite on this point the opinion of M. Fremy, whose researches in conjunction with M. Becquerel on ozone have already been referred to. "Without denying," he remarked at a meeting of the Academy of Sciences in 1865, "the importance of the indications given by the paper of M. Schonbein, or by that of M. Houzeau, I do not find that these reactions demonstrate with sufficient certainty the existence ol atmospheric ozone. I am of opinion that the presence of ozone in the air must be established anew by incontestable experiments"

In 1867 I made a set of experiments which I had contemplated some years before for the purpose, if possible, of finally settling this important question. The method I proposed was to ascertain whether, in addition to the power of decomposing solutions of iodide of potassium and of certain other salts, the active body in the atmosphere possessed the other properties of » ozone, some of which are highly distinctive. The inquiry was a delicate one, in consequence of the very minute quantity of the active body which is present, even under the most favourable conditions, in atmospheric air. The results of this investigation are given in a short note which was published in the "Proceedings of the Royal Society " for 1867. (1) By passing a stream of atmospheric air, which gave the usual reaction with iodide of potassium paper, for some hours over the surface of mercury in a U-tube, the metal was distinctly oxidised. (2.) The ozone reactions disappeared when the air was passed through a tube containing pellets of dry oxide of manganese. The experiment was continued till 80 litres of air had traversed the manganese tube without producing the slightest discoloration of a delicate test-paper. (3.) But the crucial experiment was to ascertain whether the active body in the air loses its characteristic properties, or is destroyed, at the same temperature (2370 C.) as ozone. To determine this point, a stream of atmospheric air, which gave strong ozone reactions, was passed through a globular glass vessel (Fig. 5), covered with wire gauze, of 5 litres capacity, and afterwards through a U-tube 1 metre in length, whose sides were moistened internally with water, while the tube itself was kept cool by being immersed in a vessel of cold water. After traversing the globular vessel and the moistened U-tube, the air was blown over a slip of delicate test-paper, in order to ascertain the presence or absence of ozone. When the atmospheric air was drawn through this apparatus at a uniform rate by means of an aspirator raised by clockwork, the iodide of potassium paper was distinctly reddened in two or three minutes, provided no heat was applied to the glass globe. But on heating the air as it passed through the globe, to a temperature of about 260° C., not the slightest action was produced on the paper, however long the current of air continued to pass. On the other hand, when air free from ozone, but containing traces of chlorine or of the higher oxides of nitrogen, was drawn through the apparatus, the test-papers were equally affected, whether the globe was heated or not. These experiments have since been successfully repeated by Dr. C. Fox.

The identity of the active body in the atmosphere with ozone we may now assume to be established beyond dispute, and the accuracy of Schonbein's views on this subject to be fully con

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